Background: There are some reports on the association between air pollution and myocardial infarction, arrhythmia, and mortality due to cardiac problems in susceptible individuals. We aimed to evaluate the association of air pollution and the emergency visits due to cardiovascular diseases, in a specialized heart hospital in Tehran. Methods: The study design was cross-sectional. Patients admitted to the emergency ward of Tehran Heart Center were consecutively included. Records of meteorological data for the study period were obtained from Air Quality Control Company that monitors the concentration of air pollutants through its several stations including one near to Tehran Heart Center. The principal component analysis was used to examine the association between daily air pollution level and the number of patients admitted as a result of unstable angina, myocardial infarction, and arrhythmia. Results: The principal component score -reflecting the daily air pollution level- was higher on the admission date of the patients who died in hospital compared to that of the patients who discharged alive from the hospital and the difference was statistically significant. After adjustment for the effect of age, sex, smoking, hypertension, hyperlipidemia and diabetes, a statistically significant relationship between principal component score and the unstable angina and arrhythmia was detected in patients referred to the emergency department. Conclusion: Air pollution was associated with the unstable angina and arrhythmia in patients referred to the emergency department of Tehran Heart Center, adjusted for the effect of other risk factors.